Secretary of State John Kerry issued a warning to Russian foreign minister Sergey Lavrov on Friday afternoon, urging compliance with the agreement reached in Geneva this week.

Under that pact, Russian troops would withdraw from government buildings in eastern Ukraine and take other steps to de-escalate the crisis, which began more than two months ago.

“He made clear that the next few days would be a pivotal period for all sides to implement the statement’s provisions, particularly that all illegal armed groups must be disarmed and all illegally seized buildings must be returned to legitimate owners,” a senior State Department official said.

Kerry also called Ukrainian Prime Minister Arseniy Yatsenyuk to praise steps the country has taken to implement the agreement.